Recently, there is an increasing need for air quality control of a living environment such as sterilization and deodorization, due to increased risk of infection such as seen in an increase in carriers of atopy, asthma, and allergic symptoms and explosive prevalence of new influenza. In addition, as living becomes rich, an amount of food storage and a chance of storing leftover food are increased. Accordingly, the importance of environmental control in storage equipment represented as a refrigerator is also growing.
In the prior art for the purpose of controlling air quality of a living environment, physical control as represented by a filter is generally used. According to the physical control, relatively large dust and debris floating in the air may be captured, and bacteria, viruses, or the like may also be captured depending on the size of a filter hole. In addition, when there are an infinite number of adsorption sites such activated carbon, it may also be possible to capture malodorous molecules. However, there are problems in that air in a space to be controlled is required to evenly pass through the filter in order to be captured, the apparatus is increased in size, and a maintenance cost such as filter replacement is also increased while it has no effect on adhesive substances. Therefore, as a means to enable sterilization and deodorization of adhesive substances, it may be exemplified to release chemically active species to a space desired to perform sterilization and deodorization. In spraying of chemicals or release of flavoring agents or deodorant, it is necessary to prepare the active species in advance and regular replenishment thereof is essential. On the other hand, a means to perform sterilization and deodorization using the chemically active species generated by generating plasma in the atmosphere is increased in recent years.
Technologies to perform sterilization and deodorization by ions and radicals (hereinafter, referred to as “active species”) generated by discharge of plasma into the atmosphere may be classified into the following two types:
(1) a so-called passive type plasma generator in which bacteria and viruses floating in the atmosphere (hereinafter, referred to as “floating bacteria”) or malodorous substances (hereinafter, referred to as “odor”) react with active species within a limited capacity in the apparatus (for example, Patent Document 1); and
(2) a so-called active type plasma generator in which active species generated by a plasma generating portion are released into a closed space (e.g., a living room, a toilet, a car interior, or the like) having a larger capacity than (1) released into, and the active species in the atmosphere react with floating bacteria and odor by a collision therewith (for example, Patent Document 2).
The passive type plasma generator of (1) has an advantage that high sterilization and deodorization effects may be expected because active species of high concentration are generated by generation of plasma in the small capacity. On the other hand, the apparatus has a disadvantage that the size thereof is increased because floating bacteria and odor are required to be introduced into the apparatus, and a filter for adsorption or decomposition is required to be separately installed in order to prevent ozone from leaking out of the apparatus since the ozone is likely to occur as a by-product from plasma generation.
Next, the active type plasma generator of (2) has an advantage that the apparatus may be relatively small, and sterilization of bacteria adhered to a surface of clothing (hereinafter, referred to as “adhesive bacteria”) and decomposition of odor adsorbed onto the surface may be expected in addition to sterilization of floating bacteria and decomposition of odor in the air. On the other hand, the apparatus has a disadvantage that only long-lived active species cannot help but expect sterilization and deodorization effects because active species are diffused within the closed space, which is very large compared to the volume of the apparatus, and have low concentration. As a result, the deodorization effect may not be nearly expected in a space having high odor concentration (high concentration 10,000 times the concentration of active species).
From the above, in the passive type plasma generator, the effect is limited only to floating bacteria and odor contained in an air stream flowing into the apparatus. On the other hand, in the active type plasma generator, the effect cannot help but be expected only with respect to floating bacteria, adhesive bacteria, and odor having low concentration. In other words, only either “sterilization and deodorization of floating bacteria” or “sterilization of floating bacteria and adhesive bacteria having low concentration and deodorization of adhesive odor” may be realized using the prior art.
However, there are some situations where sterilization of adhesive bacteria having high concentration and deodorization of odor having high concentration are required to be simultaneously performed in a daily life environment. The most typical example is a refrigerating chamber of a refrigerator in which many bacteria adhered to surfaces of food and a storage container surfaces exist and odor arising from food itself and decayed leftover food also exists.